The present invention relates generally to integrated circuit (IC) fabrication equipment. More particularly, the present invention relates to an attenuated phase shift mask and a method of manufacturing an attenuated phase shift mask.
Semiconductor fabrication techniques often utilize a mask or reticle. Radiation is provided through or reflected off the mask or reticle to form an image on a semiconductor wafer. The wafer is positioned to receive the radiation transmitted through or reflected off the mask or reticle. The image on the wafer corresponds to the pattern on the mask or reticle. The radiation can be light, such as ultraviolet light, vacuum ultraviolet (VUV) light, extreme ultraviolet light (EUV) and deep ultraviolet light. The radiation can also be x-ray radiation, e-beam radiation, etc.
One advanced form of lithography is extreme ultraviolet (EUV) light lithography. A conventional EUV system (e.g., an optical reduction camera or stepper) utilizes an EUV radiation source, an EUV lens assembly (e.g., a condenser lens), an EUV reticle, and another EUV lens assembly (e.g., an objective lens). EUV radiation can be created at the radiation source and projected onto the reticle. The EUV reticle is typically a resonant-reflective medium including a pattern of absorbing material. The resonant-EUV reflects a substantial portion of the EUV radiation which carries an IC pattern formed on the reticle to the second EUV lens assembly. The lens assemblies can be an all resonant-reflective imaging system including aspheric optics at 4:1 magnification factor (e.g., a series of high precision mirrors). EUV radiation reflected off the EUV reticle is provided from the second EUV lens assembly to a photoresist coated wafer.
Generally, the reticle does not include a pellicle due to the lack of transparent material at EUV wavelengths. A demagnified image of the reticle pattern is projected onto portions of the resist-coated wafer. The entire reticle pattern is exposed onto the wafer by synchronously scanning the mask and the wafer (i.e., a step-and-scan exposure).
EUV lithography utilizes radiation in a wavelength of 5 to 70 nanometers (e.g., 11-14 nanometers). A conventional EUV lithographic system or EUV stepper provides the EUV reticle as a multilayer coated reflective mask or reticle which has an absorber pattern across its surface. The multilayer coated reflective reticle can utilize molybdenum/silicon (Moxe2x80x94Si) layers or molybdenum/beryllium layers (Moxe2x80x94Be).
Attenuated phase shift masks have been employed in less advanced lithography than EUV lithography. The attenuated phase shift masks provide resolution enhancement by reducing diffractive effects. Phase shift mask approaches have been discussed thoroughly in the literature. Phase shift mask technology is discussed in the following article: M. D. Levenson et al., xe2x80x9cImproving Resolution in Photolithography with a Phase-Shifting Mask,xe2x80x9d IEEE Transactions on Electron Devices, Vol. ED-29, No. 12, pp. 1828-1836 (December 1982).
Attenuated phase shift masks (APSMs) have been disclosed that employ a thin layer which is partially light transmissive and effects a phase shift at the wavefront of the light. One such approach uses a thin layer of chromium (e.g., a few hundred angstroms, 100-300 xc3x85), while a second such approach uses a chromium oxide. The locally modified portions also provide a phase shift to the reflected light at actinic wavelength, compared to the non-locally modified portion. In the first approach, a 30 nm thick layer of chromium and dry-etching into quartz (0.42 micrometers deep) is used to achieve 180 degree phase shift. In the second approach, a thicker layer of a chromium oxide, on the order of 200 nm, and an isotropic etch into the quartz substrate, (0.04 micrometers deep), is used to achieve 180 degree phase shifts. The foregoing values are based on using i-line wavelength (365 nm).
Although attenuated phase shift masks have been utilized in less advanced lithographic applications, an attenuated phase shift mask for EUV lithography has not been practicably achieved. As discussed above, attenuated phase shift masks can be created by placing a thin layer of material on the mask to provide subphase shift to the wavefront of the radiation. In EUV applications, the thin layer can be placed between an absorbent material and the substrate. However, this technique of using a thin layer between the absorbent material and the substrate is extremely difficult because the required thickness for the thin layer is so small in EUV applications. The thickness is related to the wavelength of light which is extremely small (often 5-14 nm) in EUV applications. Depositing the thin layer within such tight specification tolerances is not practicable. In addition, etching the thin layer is very difficult to control within the tight specification tolerances. Thus, a phase shift mask for EUV applications is not practicably available.
Thus, there is a need for an attenuated phase shift mask or reticle which can be utilized in EUV applications. Further, there is a need for an attenuated phase shift mask which can be easily manufactured. Further still, there is a need for an attenuated phase shift mask or reticle optimized for use in EUV applications or advanced lithography.
An embodiment relates to an attenuated phase shift mask for integrated circuit fabrication equipment. The attenuated phase shift mask includes a multilayer film relatively reflective to radiation having a wavelength of 70 nanometers or less. The multilayer film has locally modified portions. The locally modified portions are differently reflective at actinic wavelengths than non-locally modified portions.
Another embodiment relates to an attenuated phase shift mask for fabrication equipment. The mask includes means for reflecting radiation and means for attenuating and phase shifting the radiation. The means for attenuating and phase shifting and the means for reflecting are disposed on a same surface.
Yet another embodiment relates to a method of manufacturing a phase shift mask. The method includes providing a multilayer film on a substrate, providing a heat mask over the multilayer film, and selectively etching the heat mask to form a pattern. The method also includes heat treating the multilayer film in accordance with the heat mask.
Still another embodiment relates to a reticle or photomask for use with EUV radiation. The reticle or photomask provides locally attenuated phase shifting at actinic wavelengths in the EUV range.